The Early Universe Molecular Emission Line Galaxies (EMGs) are a population of galaxies with only 36 examples that hold great promise for the study of galaxy formation and evolution at high redshift. The classification, luminosity of molecular line emission, molecular mass, far-infrared (FIR) luminosity, star formation efficiency, morphology, and dynamical mass of the currently known sample are presented and discussed. The star formation rates derived from the FIR luminosity range from about 300 to 5000 M⊙ year −1 and the molecular mass from 4 × 10 9 to 1 × 10 11 M⊙. At the lower end, these star formation rates, gas masses, and diameters are similar to those of local ultraluminous infrared galaxies, and represent starbursts in centrally concentrated disks, sometimes, but not always, associated with active galactic nuclei.

ALMA observations of the long wavelength dust continuum are used to estimate the interstellar medium (ISM) masses in a sample of 708 galaxies at z=0.3 to 4.5 in the COSMOS field. The galaxy sample has known farinfrared luminosities and, hence, star formation rates (SFRs) and stellar masses ( * M ) from the optical-infrared spectrum fitting. The galaxies sample SFRs from the main sequence (MS) to 50 times above the MS. The derived ISM masses are used to determine the dependence of gas mass on redshift, * M , and specific SFR (sSFR) relative to the MS. The ISM masses increase approximately with the 0.63 power of the rate of increase in SFRs with redshift and the 0.32 power of the sSFR/sSFR MS . The SF efficiencies also increase as the 0.36 power of the SFR redshift evolution and the 0.7 power of the elevation above the MS; thus the increased activities at early epochs are driven by both increased ISM masses and SF efficiency. Using the derived ISM mass function, we estimate the accretion rates of gas required to maintain continuity of the MS evolution (>  M 100 yr −1 at z > 2.5). Simple power-law dependencies are similarly derived for the gas accretion rates. We argue that the overall evolution of galaxies is driven by the rates of gas accretion. The cosmic evolution of total ISM mass is estimated and linked to the evolution of SF and active galactic nucleus activity at early epochs.

ALMA Cycle 2 observations of the long wavelength dust emission in 145 star-forming galaxies are used to probe the evolution of star-forming ISM. We also develop the physical basis and empirical calibration (with 72 low-z and z ∼2 galaxies) for using the dust continuum as a quantitative probe of interstellar medium (ISM) masses. The galaxies with highest star formation rates (SFRs) at < z > = 2.2 and 4.4 have gas masses up to 100 times that of the Milky Way and gas mass fractions reaching 50 to 80%, i.e. gas masses 1 -4 × their stellar masses. We find a single high-z star formation law:-an approximately linear dependence on the ISM mass and an increased star formation efficiency per unit gas mass at higher redshift. Galaxies above the Main Sequence (MS) have larger gas masses but are converting their ISM into stars on a timescale only slightly shorter than those on the MS -thus these 'starbursts' are largely the result of having greatly increased gas masses rather than and increased efficiency for converting gas to stars. At z > 1, the entire population of star-forming galaxies has ∼ 2 -5 times shorter gas depletion times than low-z galaxies. These shorter depletion times indicate a different mode of star formation in the early universe -most likely dynamically driven by compressive, high-dispersion gas motions -a natural consequence of the high gas accretion rates.

No abstract

Observations have revealed prodigious amounts of star formation in starburst galaxies as traced by dust and molecular emission, even at large redshifts. Recent work shows that for both nearby spiral galaxies and distant starbursts, the global star formation rate, as indicated by the infrared luminosity, has a tight and almost linear correlation with the amount of dense gas as traced by the luminosity of HCN. Our surveys of Galactic dense cores in HCN 1−0 emission show that this correlation continues to a much smaller scale, with nearly the same ratio of infrared luminosity to HCN luminosity found over 7-8 orders of magnitude in L IR , with a lower cutoff around 10 4.5 L ⊙ of infrared luminosity. The linear correlation suggests that we may understand distant star formation in terms of the known properties of local star-forming regions. Both the correlation and the luminosity cutoff can be explained if the basic unit of star formation in galaxies is a dense core, similar to those studied in our Galaxy.